This invention relates to a heater for an oven with a conveyor, and more particularly to a heating system for use with a liquid dispensing system.
In the manufacture of printed circuit boards, liquid dispensing systems can be used to dispense liquids on the circuit board. Different types of dispensers can be used to dispense different types of liquids for different purposes. One application of a liquid dispenser is for dispensing glue for mounting components on the board. Another application for a liquid dispenser arises after a packaged chip has been mounted to a circuit board. The liquid dispenser dispenses a bead of liquid around the perimeter of the chip. The liquid wicks under the chip to underfill it, thereby thermally conducting heat away from the packaged chip. In another application, a die can be mounted to a circuit board, and then the liquid dispenser dispenses a viscous liquid over the die. The liquid hardens to encapsulate the die in place on the board. In such liquid dispensing systems, a conveyor transports a circuit board along a direction of travel until it reaches a desired position where the conveyor stops and the dispensing is performed.
The underfill and encapsulation processes are typically performed in a heated environment. A radiant heater heats the circuit board from below while the liquid dispenser dispenses liquid from above. One type of heater has a number of quartz tubes mounted in parallel, transverse to the direction of travel. The quartz tubes enclose coils that quickly heat to a high temperature with an electric current. These tubes, however, tend to create relatively hotter and relative cooler areas on a circuit board.
In ovens used for reflow soldering, convection can be added to the radiant heating by providing a fan to blow air across the radiant heat source. A plate with a series of holes is positioned between the fan and the radiant heat source, or the radiant heat source can itself be a panel with holes. Because of the circular air flow from the fan, however, the temperature of the air that flows through the openings is inconsistent from one hole or group of holes to others. Another drawback with such a system is that the fan pushes a large volume of hot air that provides great heat to the outside environment.